1. Field of the Invention
This invention relates to an image forming apparatus which uses a screen-like photosensitive medium having a multitude of tiny openings therein (hereinafter referred to as "photosensitive screen"). More particularly, it relates to an image forming apparatus which uses a photosensitive screen to enable copy images to be produced at a high speed.
2. Description of the Prior Art
Electrophotographic methods using photosensitive screens are disclosed in Japanese Patent Publication No. 21142/1972, U.S. Pat. No. 3,680,954, etc. The electrophotographic method described in said Japanese Patent Publication involves the steps of uniformly charging the surface of a photosensitive screen having a multitude of openings therein and comprising an electrically conductive back-up member and a photoconductive layer, then projecting an original image upon the photosensitive screen, and forming on the screen an electrostatic latent image corresponding to the original image (hereinafter referred to as "primary electrostatic latent image"). Thereafter, a recording member having a chargeable layer is disposed and held in a predetermined spaced-apart and opposed relationship with the screen surface bearing the primary electrostatic latent image. Corona discharge is then applied to the surface of the recording member through the photosensitive screen, whereby an ion flow is modulated by the electric field of the primary electrostatic latent image to form on the recording member an electrostatic latent image corresponding to the original image (hereinafter referred to as "secondary electrostatic latent image"). The secondary electrostatic latent image formed in the described manner is thereafter developed into a visible image by a developing technique commonly used in the known electrophotographic method. The method disclosed in U.S. Pat. No. 3,680,954 differs in construction of the photosensitive screen, but it may be said to be a similar art that such screen is used for the image formation.
With conventional apparatus of the type wherein a secondary electrostatic latent image is formed repetitively from a common primary electrostatic latent image, formation of the secondary electrostatic latent image has been done either by stopping a planar photosensitive screen, opposed to which a recording member is temporarily stopped with a flat surface of a predetermined length, while moving a corona discharger or by moving the photosensitive screen and the recording member in the same direction and at the same velocity while using a stationary corona discharger. The former system has required some time for interchange of the recording member, and the latter system has also required the recording member not to be fed until the screen is restored to its initial position. The planar photosensitive screen is thus easy and simple to make, whereas an apparatus using such a planar photosensitive screen has encountered problems in forming secondary electrostatic latent images at a high speed.